1. Field of the Invention
This invention relates to the transmission of handwriting or graphics intelligence; and to the terminals of stations that transmit and receive and reproduce such data.
2. Description of the Prior Art
In the earlier U.S. Pat. No. 3,706,850 issued Dec. 19, 1972, and assigned to applicants' assignee, there is described a telewriting system for transmitting handwriting and similar data in real time over voice grade telephone lines. In this system the reproduction of the data at a remote location is achieved by a laser that forms graphics information on a film in accordance with incoming scanning signals.
This system and others like it have significant potential use as a medium for remote teaching and teleconferencing. As with all such telewriting systems and equipment, its acceptance depends on ease of use, cost, and the presence of features that faithfully and reliably replicate the graphics information.
For example, systems requiring only a single telephone line make possible the employment of far less expensive data modems which do not require simultaneous duplex transmission. Additionally, it is useful for such a system to communicate simultaneously to several receiving stations and to provide at each such station several -- for example three -- viewing stations. Considerations of cost suggest that these stations be ordinary television monitors.
Among the telewriting systems features desired but currently unavailable, is provision for distinguishing circuit noise or otherwise bogus signals from genuine graphics. The faithful reproduction of the originating graphics signal such as one written on a remote blackboard of the type described in U.S. Pat. No. 3,959,585 and assigned to applicants' assignee, depends in part on reducing the effects of noise. Good reproduction also depends on graphics signal value sampling in which the X and Y samples are sufficiently close in time to each other to avoid the equivalent of phase distortion which can disconfigure the received writing.
Partial and full erasing features likewise are desired but not reliably available in existing graphics transmission systems. Additionally, the use of tape recorders with electronic blackboard systems in the prior art has not fully addressed the problem of signal distortion due to jitter and other factors.